Field of the Invention
The present invention relates to a method of initializing a phase-change optical disk which permits an information signal to be recorded/reproduced when irradiated with a laser beam and to a phase-change optical disk adaptable to the initializing method.
A phase-change optical disk of a type which permits an information signal to be recorded/reproduced when irradiated with a laser beam has been suggested.
As shown in FIG. 1, a phase-change optical disk 10 of the foregoing type has the main surface of a transparent substrate 11 made of a plastic, such as polycarbonate. On the main surface of the transparent substrate 11, there are formed multi-layered films 12 to 16 which are functional films including a first dielectric layer 12, a phase-change material layer 13, a second dielectric layer 14, a reflecting layer 15 and a protective film 16. The multi-layered films 12 to 16 are formed by application processes.
As shown in FIG. 2, the phase-change optical disk 10 uses the multi-layered films 12 to 16 as surfaces on which information signals are recorded. The difference between the reflectance of crystal of the phase-change material and that of amorphous phases is used to record/reproduce the information signal. That is, amorphous marks 2 and crystal spaces 1 are formed along tracks formed on the surface on which an information signal will be recorded. Thus, an information signal can be recorded, and the recorded information signal can be read.
The phase-change optical disk 10 is different from a magneto-optical disk in that no external magnetic field need be applied to the phase-change optical disk 10 when an information signal is recorded or reproduced. Therefore, magnetic heads and the like are not required to record or reproduce an information signal. Thus, considerable research of the phase-change optical disk has been done because of great expectations for a next-generation information recording medium.
The phase-change optical disk 10 having the above-mentioned structure has a surface, on which an information signal will be recorded that, must be initialized before a user uses the phase-change optical disk 10.
The multi-layered films 12 to 16 forming the surface of the phase-change optical disk 10, on which an information signal will be recorded, are usually formed by application processes, for example, sputtering. Therefore, the surface of the phase-change optical disk 10 having the multi-layered films 12 to 16, on which information signals will be recorded, must temporarily be crystallized by an appropriate method.
FIG. 3 shows a portion of the surface of the phase-change optical disk 10, on which information signals will be recorded and which has fully crystallized by an initializing process. The surface, on which information signals will be recorded, has grooves 3 and lands 4 both of which have been crystallized so that spaces 1 are created.
As shown in FIG. 4, a portion of the phase-change optical disks 10 having the surface, on which information signal will be recorded and the overall surface of which has been crystallized, has regular information signals in order to inspect the signal characteristic of the surface on which information signal will be recorded. As an alternative to this, another portion of the phase-change optical disks 10 has irregular information signals, as shown in FIG. 5.
Since the information signal arranged to be recorded on the phase-change optical disk 10 conforms to a so-called EFM-modulation format, the length ML of each mark and the length SL of each space fall within a range from 3T to 11T when T indicates a unit period.
The phase-change optical disk 10, which has been initialized by crystallization of the overall surface on which information signal will be recorded or by recording appropriate information signals on the surface on which information signal will be recorded, suffers from a problem in that the amount of jitter increases until overwriting is performed about ten times.
Enlargement of the amount of jitter is generally detrimental to the accuracy of the information signal and to the stability of the apparatus. It is ideal that the amount of jitter is not higher than 10%.
In view of the foregoing, an object of the present invention is to provide a method of initializing a phase-change optical disk which is capable of preventing an increases in the amount of jitter which takes place when the number of overwriting operations does not exceed about ten times, and to provide a phase-change optical disk.
To achieve the above-mentioned object, according to one aspect of the present invention, there is provided a method of initializing a phase-change optical disk comprising: a crystallizing step for crystallizing recording regions formed on the main surface of a disk; and a recording step for recording at least marks along tracks by irradiating the recording regions with laser beams, wherein the length of each of spaces formed between the marks along the tracks is shorter than a shortest length of spaces each of which is formed between information signals which will be recorded on the recording regions.
The above-mentioned method of initializing a phase-change optical disk has the crystallizing step in which the recording regions formed on the main surface of the disk are crystallized. In the recording step, marks are recorded in the recording regions along the tracks by performing irradiation with laser beams. When the initialization is performed, the length of each of the spaces formed between the marks is made to be shorter than a shortest length of spaces formed between information signals. It is preferable that the space between the marks be shorter than the shortest recording wavelength or that no space is formed.
The method of initializing a phase-change optical disk according to the present invention is arranged in such a manner that the recording step uses irradiation with pulse signals.
The method of initializing a phase-change optical disk according to the present invention has a structure that the recording step is performed in such a manner that continuous molten amorphous regions are formed along the tracks of the recording regions by performing irradiation with DC light beams.
According to another aspect of the present invention, there is provided a phase-change optical disk comprising: a disk having a main surface on which recording regions are formed; and at least marks formed in the recording regions along tracks, wherein the length of each of spaces formed between the marks along the tracks is shorter than a shortest length of spaces formed between information signals which will be recorded on the recording regions.
The phase-change optical disk is arranged in such a manner that the marks having spaces which are shorter than the shortest space between information signals are formed along tracks in the recording regions formed on the main surface of the disk.
The phase-change optical disk according to the present invention has a structure that the marks are continuously recorded on the recording regions.
The phase-change optical disk according to the present invention has a structure that the marks are continuously recorded along the tracks in the recording regions formed on the main surface of the disk.
Other and further objects, features and advantage of the invention will be appear more fully from the following description.